1. Field of the Invention
This invention relates generally to the navigation displays provided by an electronic flight instrument system and, more particularly, to the arc mode and the Rose Nav mode of the navigation display.
2. Description of the Related Art
In the present navigation display of the electronic flight instrumentation system, the operator has the option of choosing from a plurality of display screens. Referring to FIG. 1A, an arc mode (also referred to as the map mode) navigation display screen is illustrated. In this display mode, the flight of the aircraft is always oriented perpendicular to the top of the display screen. The arc mode navigation display screen includes an Edit area 10. The Edit area 10 of the arc mode navigation display screen exceeds the boundaries of the display device screen, the boundaries of the display screen coinciding with the viewable boundary 16. The Edit area is the area of the display that is the analog of the ground area for which information is required. The Edit area is determined by a controllable range setting and can, for example, be 10 nautical miles (nm), 20 nm, 40 nm, 80 nm, 160 nm and 320 nm. However, in the prior art arc (and Rose Nav) display mode, the feature determination was performed for the modified Edit area enclosed within boundary 19. Boundary 19 has a rectangular configuration passing through the corner points of the Edit area and oriented with respect to the North direction. The location of the aircraft is indicated on the display area by aircraft icon 11. The aircraft icon 11 is located at the map reference point (MRP), a fixed point on the display For the arc mode display screen, the map reference point and the aircraft icon are coincident The dashed vertical arrow 3 from the aircraft icon 11 to the top of the Edit area is coincident with the current heading of the aircraft. The direction of the current heading is known to the display apparatus from sensor and/or navigational apparatus (such as a gyroscope). The dashed vertical arrow 4 from the aircraft icon 11 to the bottom of the Edit area is in the opposite direction from the current heading arrow 3. The horizontal dashed arrows 2 to the sides of the Edit area 10 are perpendicular to the current heading. The length of the current heading arrow 3 is typically longer than dashed arrow 4 permitting features to be displayed over a greater area in front of the aircraft. The arc mode display screen also displays the planned flight path 15. The aircraft flight plan is typically specified in a multiplicity of geographical locations (i.e., latitude and longitude coordinates). These locations are entered in a multipurpose control and display unit and are displayed as icons on the navigation display screen. In FIG. 1A, the geographical location icons 12 are triangles.
Referring next to FIG. 1B, the same display screen is illustrated when the Rose Nav display mode is selected. Once again, the direction of the flight of the aircraft is always perpendicular to the top of the display screen. The display screen in this mode is the same as the display screen for the arc display in FIG. 1A with the exception that the map reference point and the aircraft icon are located in the center of the display screen, i.e., the vertical dashed arrow 3 is the same length as the reverse vertical arrow 4. In this display mode, equal emphasis is given to the features in the direction of travel of the aircraft and in the direction opposite to the direction of travel of the aircraft. In both the arc display mode and the Rose Nav display mode, the constant direction of the aircraft and the flight path direction result in a rotation of the displayed features as the aircraft flight direction changes.
Referring to FIG. 1C, the display screen shown in FIG. 1A and FIG. 1B is illustrated for the plan display mode. In this display mode, the Edit area 10 remains the same and the viewing area of the display screen is within the viewing boundary 19. However, in this display mode, the north direction is fixed in the vertical direction. Therefore, the flight path, equivalent to the flight path in FIG. 1A and FIG. 1B, is rotated. In the plan display mode, the map reference point, the center of the display, can be any selected flight path location. The airplane icon moves on the screen while the map reference point remains fixed until a further selection is made. Because the display is held constant with respect to the North direction, the Edit area is coincident with the modified Edit area.
Referring to FIG. 2, another feature of the navigation display is illustrated. In these navigation displays, data is available in the data base to provide a position of selected features that can be important in the flight of the aircraft on the display screen. For example, the locations of airports, of geographical features, of navigational aids (such as beacons) are stored in the data base and can be displayed, in response to activation by the operator, as an overlay on the display screens. In FIG. 2, icons 21 (circles), icons 23 (squares) and icons 24 (hexagons) are displayed. These icons can represent, for example, airports, geographical waypoints and nondirectional navigational beacons respectively. The icons can have alpha numeric information associated therewith identifying the icons. As the area displayed by the screen becomes larger (in response to control selection by the operator), it will be clear that an increasing number of icons will be displayed. As will be clear by comparison of the arc mode, the Rose Nav mode and the plan mode shown in FIG. 1A, FIG. 1B and FIG. 1C, respectively, the arc mode and the Rose Nav mode can have features present in the modified Edit area that can not be viewed under the current conditions. Because the Edit area and the modified Edit area are coincident in the plan mode of operations, no features will be present that are not in the Edit area.
The situation with respect to the display of icons is complicated by the storage capability of buffer storage units associated with the display apparatus controlling the display screen image. The display buffer storage unit contains the information related to features important to navigation permitting the display apparatus to provide the icons representing the important features on the display screen. The features information is, in turn, retrieved from a navigation data base unit containing all of the features information and stored in the display buffer storage unit according to a preselected algorithm The buffer memory storage unit is currently limited to 512 words, each word being 32 bits in length. Therefore, the number of icons for display on the display screen can exceed the available area in the display buffer storage unit in appropriate circumstances. More importantly, in the arc display mode and the Rose Nav display mode, feature information within the modified Edit area 19, but outside of Edit area 10 and therefore feature information that is unviewable, can be stored in the display buffer storage unit, while the more important information inside the Edit area 10 may not be displayed because of the limited capacity of the display buffer storage unit, thereby compromising the usefulness of the navigation display in the decision process.
A need has therefore been felt for a technique for maximizing the feature information that can be displayed on a navigation display screen in the Edit area while minimizing or eliminating feature information outside the Edit area in the modified Edit area.